Glass-ceramic and method for making same

ABSTRACT

High-strength glass-ceramics and a method of producing glassceramics having high strengths and good thermal shock resistance wherein a thermally crystallizable glass containing a nucleating agent capable of changing valency and which is more effective in the changed valency state is thermally in situ crystallized in a reducing atmosphere to form an at least partially crystalline glass-ceramic having a coefficient of thermal expansion which is considerably lower than that of the parent glass and having a high compressive stress layer on its surface.

mted States Patent 1 1 1 1 3,779,856 Pirooz Dec. 18, 1973 GLASS-CERAMIC AND METHOD FOR 3,231,456 1/1966 McMillan et a1. 65/33 x MAKING SAME 3,464,806 9/1969 Seki et a].

3,637,453 1/1972 Simmons 161/192 X [75] Inventor: Perry P. Pirooz, Toledo, Ohio 73] Assignee: Owens-Illinois, 1116., Toledo, Ohio Primary Examiner-Charles Van Horn AttorneyE. J. Holler et a1. [22] F1led: July 23, 1971 [21] Appl. No.: 165,744 [57] ABSTRACT High-strength glass-ceramics and a method of produc- 52 us. or 161/164, 161/1, 161/192, ihg glass-Ceramics having high Strengths and good 65/33 106/397, 106/393 106/52 thermal shock resistance wherein a thermally crystal- 511 1111.131. C030 23/00, C036 3/22 "Zable glass Containing a hucleatihg agent capable of [58] Field 61 Search 161/164, 192, 193, changing valency and which is more effective in the [61/]; 5 106/39 DV, 5 39] 39,8 changed valency state is thermally in situ crystallized in a reducing atmosphere to form an at least partially [56] References Cited crystalline glass-ceramic having a coefficient of ther- UNITED STATES PATENTS mal expansion which is considerably lower than that of the parent glass and having a high compressive 3,490,984 l/197O Petticrew ct al 161/192 X Stress layer on its surface 3,582,385 6/1971 Duke et al. 106/39 DV 3,486,963 12/1969 8 Claims, No Drawings Smith 65/33 x GLASS-CERAMIC AND METHOD FOR MAKING SAME Various methods for producing high-strength glass and glass-ceramic articles are known in the art wherein a compressive stress layer is formed on the surface of the article. The oldest of these methods is referred to as thermal tempering and is based on the quenching of theglass surface. Another methodis that known as ion exchange wherein large ions on the surface of the glass are exchanged for smaller ones, usually by contacting the glass surface with a salt solution or melt of the ions to be exchanged and maintaining such contact for the period of time necessary for the exchange to be complate and a compressive stress layer of the desired depth produced. Such depths in commercial glassceramics are usually less than 90 microns in thickness and more usually are about 20 to 50 microns in thickness. Still another method involves the cladding of a glass surfacewith another glass which is capable of forming a low-expansion crystalline phase and then heat treating the latter glass. Also, the incorporation of fluorine into certain glasses to form high-strength glassceramics therefrom by thermal in situ crystallization is known. Each of these known methods has certain disadvantages in that they can be utilized only with glasses of certain compositions or they require additional process steps which add materially to the final cost of the article produced thereby.

The present invention for forming a compressive stress layer on the surface of a glass-ceramic differs from the prior art methods in that a thermally crystallizable glass capable of being thermally in situ crystallized to a glass-ceramic having a coefficient of thermal expansion which is considerably less than that of the parent glass, preferably a difierence of at least 20 X l"/C. (0-300C.) or more, wherein the parent glass contains a nucleating agent which can have its valency changed and such changed valency state is the more effective state for nucleating the glass, is subjected to a nucleating temperature while held in a reducing atmosphere for a time sufficient for the nucleation to be substantially complete. The reducing atmosphere in contact with the surface of the glass reduces the valency of the nucleating agent at and just below the surface of the glass resulting in an increased rate of nucleation along that portion of the glass where such reduced nucleating agent is present. When subsequently crystallized, the degree of crystallinity is greater at the surface than in the interior of the article and this differential crystallization produces a compressive stress layer on the glass-ceramic surface. The depth of the layer is dependent on the difference in nucleation and the extent of that difference inwardly from the surface.

The change in valency of the nucleating agent can be enhanced if there is present in the glass an oxide of a metal which will promote the reduction of the nucleating agent when in contact with the reducing atmosphere. Oxides of copper, iron, and manganese are examples of compounds which assist in promoting the reduction of the nucleating'agent.

The preferred nucleating agents for thermally crystallizable glasses which can be thermally in situ crystallized to a glass-ceramic having a much lower coefficient of thermal expansion are TiO ZrO- and mixtures thereof. These oxides are most effective as nucleation agents dsr s eiassqsditi9 s..,.

In one embodiment of the invention it has been found that glasses of the Li O--Al O -SiO system which can be thermally in situ crystallized to low expansion, transparent, high quartz solid solution glass-ceramics and which contain a nucleating agent and CuO, can be significantly strengthened by the process of this invention. The increase in flexural strength is due to the forination of a surface compressive layer which is the result of differential crystallization of the surface versus the interior of the article. Thermally crystallizable glass systems, such as MgOAl O SiO and Na O-Al O SiO systems, wherein the resulting glass-ceramics have a higher coefficient of thermal expansion than the present glass are not suitable for the purpose of this invention.

Thermally crystallizable glasses suitable for producing transparent glass-ceramics having high flexural strengths of from about 30,000 psi to about 80,000 psi and more, having resistance to thermal shock and having good chemical durability are those wherein the essential ingredients are within the following ranges:

ingredient Weight Percent SiO, 54-76 A1 0 18-33 Li O 2.0-6.4 Nucleating Agent 3-8 CuO 0.5-6

wherein the nucleating agent is selected from the group consisting of TiO ZrO and mixtures thereof, and the molar ratio of SiO to A1 0 is from 3 to 6, and the ,molar ratio of Li O to A1 0 is from 0.3 to about 0.9. When TiO or ZrO is used as the sole nucleating agent, it is present in an amount of 3 to 6 weight percent. Use of more than about 6 weight percent or of more than about 8 weight percent of the mixture does not materi-' ally improve the crystallization process and, besides adding to the cost of the final product, may have some deleterious effects. For example, an excess of ZrO {increases the liquidus temperature of the glass and makes the glass more difficult to work. An excess of iTiO will increase the expansion coefficient of the resulting glass-ceramics, which defeats the purpose of the present invention, namely to have as much of a differ- ,ence between the thermal expansion properties of the iglass-ceramics and the present glass as possible in order to obtain the greatest compressive stress layer formed ion the surface of the glass-ceramic. I

The essential ingredients listed above must be present in an amount of at least about percent by weight of the composition and preferably at least percent ,by weight of the composition. Other metal oxides can be present in minor amounts, either singly or as mix- ;tures provided that such oxides are compatible with the iLi O-Al O SiO -CuO systems and do not adversely affect the desired properties in the final products. Exfamples of such other metal oxides are Na O, K 0, CaO, iBaO, ZnO, SnO, PbO, MgO, and the like.

While the foregoing defines the compositions broadly, in its preferred embodiment the glass-ceramic of the invention has the following composition, with "these ingredients coming within the following ranges:

Ingredients Weight Percent SiO, 57-69 A1 0, 20-3l Li o 3-6 Nuclealing Agent 3-10 CuO 1-5 the essential ingredients form at least about90 percent by weight and preferably at least 95% by weight of the compositions.

When the SiO /Al O molar ratio is in excess of about 6, the resulting glass is too viscous to be worked properly by commercial glass-forming methods. When the molar ratio is less than 3, the glass becomes too fluid and unstable and readily undergoes uncontrolled devitrification.

Upon analysis, the glasses were found to have the following indicated compositions, expressed in weight 10 percent:

TABLE ll Compositions Ingredients 1 2 3 4 5 6 7 Si02 62.2 61.1 61.1 58.7 67.9 67.9 57.2 A1 03. 26.4 26.7 26.6 26.1 21.0 21.1 30.9 LizO 4.9 4.7 4.7 4.5 3.8 3.8 5.6 Na O. 2.0 1.7 1.0 1.8 TlOz... 1.4 1.4 1.4 1.4 1.8 1.8 1.8 ZrO2.. 2.1 2.3 2.1 2.2 2.0 2.0 2.1 CuO... 1.0 .56 3.0 0.9 1.5 3.4 0.5 Cu O .24 4.2 CaO Fe O; Molar Ratio LEO/A1 0 Molar Ratio SiOdAhO Coefi. Thermal Expansion X 10- lf-lotanal yze df or Cu O. CuO is total copper oxide expressed as CuO.

Each glass was placed in an electric furnace which had been heated to 400 C. The furnace was then purged for 15 minutes with forming gas consisting of percent nitrogen and 10 percent hydrogen, by volume.

Each glass was then treated to the desired nucleating.

and crystallization temperature at a particular heating TABLE I rt 2)! .Weisht.

Compositions Ingredients 1 2 3 4 5 6 7 Ottawa Flint Sand 2842 3009 3060 2656 3133 3132 2809 Alcoa Alumina A-lO. 1322 1332 1338 1277 1056 1056 1535 Lithium Carbonate 489 590 525 437 354 357 696 Lithium Zirconate.... 143

Titanox Cupric Oxide High Calcium Lime Melting Temperature (C.) Melting Time (Hours)...

37.5 24 over- 25.5

night *Glass Frit consisted of, by weight, 24.41% grQ 64.2 2% i0 and l 1.38% Li O.

rate, held there for the desired time and finally cooled. to room temperature at the normal furnace rate.

The heat treatment schedules and the physical property measurements for each of the glasses are set forth tallized in air, no compression layer formed on the surface. Note also that the glasses of the invention initially crystallize on the surface, and if the heat treatment is stopped at this point the product is essentially a relan the followlng table: a g v tively high expansion glass, with a low expansion com- TABLE III Heat-treatment conditions Properties Heating Holding Forming Comp Rate Temp. Time Gas or a X Comp. Stress Depth No. g g/ r. "c (hrs.) Air (0300 Q p.s.i. 10* (pm) 320 800 4 F.G. 1.8 49.6 170 320 800 16 F.G. 3.9 28.5 200 *max. 800 16 air 2.8 0) 320 800 4 F.G. 2.7 35.8 140 320 775 8 F.G. 1.7 53.0 203 1 320 775 16 F.G. 3.1 21.0 360 320 775 0 F.G. 43.2 48.0 100 320 775 2 F.G. 4.7' 72.0 224 320 775 4 F.G. 6.l 45.0 200 320 800 2 F.G. 7.1 35.0 168 320 750 16 F.G. 7.7il 59.0 375 320 825 2 F.G. 3.4 i 38.0 185 max. 800 2 F.G. 4.7 56.0 196 320 800 2 F.G. 10.2 i 26.0 190 max. 800 4 F.G. 11.8 40.0 224 max. 850 4 F.G. 10.4 58.0 207 320 775 8 PG. 9.4 52.7 336 320 775 16 F.G. 10.6 32.0 224 320 775 24 F.G. 10.3 36.7 290 320 775 4 F.G. 1.4 46.0 324 320 775 4 F.G. 2.9 36.0 195 320 775 8 F.G. -6.0 20.0 140 320 775 16 F.G. 8.8 31.0 168 320 775 24 F.G. 9.4 42.8 250 means tths um sq.wasfirsthsated1t? th hq instsmve an 1s. glass then placed therein at that temperature and held for the indicated holding time.

. .T N ssmare s s.. ttsalaxstw firmed- Composition No. 4 was heat treated by holding one hour at 775C. in an atmosphere of H 0 to form the will produce a compressive stress layer on the surface when given the proper heat treatment and that the results which are obtained are sensitive to such heat treatment. While from about 0.5 to about 6% CuO can be present in the Li OAl O SiO- glasses, it is preferable to have the CuO content be from about 1 to about 3.5%. Optimum results can be obtained when the amount of CuO is about 3% by weight.

Compressive stresses of from about 30,000 psi up to 80,000 psi and more can be'obtained by the process of this invention. Preferably stresses of about 50,000 to 80,000 psi or more can be imparted to the transparent glass-ceramics of the invention by appropriate adjust-- ment of the compositions, the heating times, and the heating temperatures.

While the glass ceramics which are formed are transparent, it is to be understood that when the ceramic is} of substantial thickness, some haziness or cloudiness} may appear, due to the light scattering which occurs,

so that instead of being truly transparent, like window 6 pressive layer on the surface (see the last heat treatment of composition No. 2).

While the reducing atmosphere utilized in producing the high-strength glass-ceramics of the invention exemplified in Table III was forming gas, which is readily available commercially and consists of nitrogen and 10% hydrogen by volume, other reducing atmosphere can be utilized for the purpose of the invention. Thus mixtures of nitrogen and hydrogen in different proportions, carbon monoxide, steam, natural gas, and

the like, or mixtures of two or moreof such gases can be used. 1

For example, two glasses of Composition No. 2 were heated in an atmosphere of steam at a heat-up rate of 320C./hour until the holding temperature of 775C. and 800C, respectively, were reached, and then held at such temperature for 1 hour and cooled to room temperature at furnace rate. The moduli of rupture for the glass-ceramics were 46,800 psi and 63,000 psi, re-

spectively.

Modulus of rupture tests were conducted on two of the glasses of Table 111 to show that glass-ceramics having high compressive stress layers also have high moduli of rupture, and the results are set forth below in 11 219 Forming Comp. Heat Treatment Gas M.O.R.

No. Temp. C.(hrs) or Air X10 Abraded 6 not heat treated 17.2 no 6 not heat treated 10.3 yes 6 825(1) F.G. 64.7 no 6 .825(1) F.G. 56.9 yes 6 875(1) F.G. 69.5 no 6 740 (16) 850(1) air 10.4 no 3 775 (2) F.G. 74.5 no 3 775 (2 F.G. 56.5 yes All samples in Table IV were heated at a heat-up rate of 320 C./hour to the indicated holding temperatures and held for the indicated times. They were then cooled to ambient temperature at the furnace rate. All modulus of rupture measurements were made on 5 X 0.2 inch cane samples which were either abraded or unabraded, using either the lnstron or the Tinius-Olsen measuring instruments. Each value set forth in Table IV is based on the average of five samples with the exception of the composition heat treated in air which is based upon seven samples. Abrasion was performed by placing the rods in a ball mill containing 240 grit and milling for 15 minutes.

Iron, another transition metal element, was used in lieu of copper in the glass of Composition 8. Since iron can readily change its valence state when present in a Weight Percent Total Fe,0, FeO as FcO/FqO,

Fe o Composition No. 8 0.66 L67 2.5l 2.5 Composition No. 8 (oxygenated) L29 l.07 2.48 0.8

glass, a comparison of its effect was made by adding 1 ged pieces.

. TABL v 4. (Weight Percent) Compositions Ingredients 8 9 10 l l I2 13 14 SiOz... 66.8 66.8 64.4 63.0 64.4 63.0 Algog. 20.6 LizO... .8 Na O. TiO Zr CuO... Cu O.. CaO Fe O (Si).....

MgO..

V 0 Molar Ratio LEO/M 0 0.6 0.62 0.62 0.62 Molar Ratio SlOpjAlzOa 5.5 5.5 5.35 4.4 4.4 4.4 4.4 Coeff. Thermal Expansion X 39.5 36.3 35.2 37.5 39.5 39.7 39.5

*Iron oxide expressed as Fe O3.

TABLE v1 7 7 Heat-treatment conditions P -fi Heating Holding Forming Comp l l ae Te np. Time Gas or a X l0 Comp. Stress Depth No. (C/hi C (hrs.) Air (0-300 C p.s.i. X 10 (um) 320 750 16 EC. 0.9 15.0 10 320 775 2 F.G. l.9 21.0 3 320 825 2 F.G. 0.4 33.0 5

Glass remelted for 24 hours during which time oxygen gas was bubbled through the melt mole percent of Fe O to the base glass used for Com- 7 5 Examples 9 and l0 illustrate forming a compressive chemical an analysis shows the effect of melting conditions on the oxidation state of the iron.

layer according to the invention in compositions containing either TiO alone as a nucleant or ZrO alone as a nucleant. Heat treatment conditions are given below in Table VlA.

TABLE VIA Comp. Heating Holding Time AtmosaXlO" No Rate Temp. (hrs) pheric (03()0C) (C/hr) C 9 max. 750 16 F.G. 7 320 850 1 EC. 6

Other known nucleating agents were substituted for gla s ses to ascertain their behavior. SnO was used as a nucleant in the glasses of Examples 1 l and 12. When heat treated at about TABLE Vll Compositions by Weight Percent Ingredients l5 l6 l7 l8 900C, a low-expansion opaque body (12 X 10") sio, 69.3 67.5 66.6 65.8 was produced which consisted primarily of a high- 5 338* 5;; 2:2 2-8 quartz solid solution phase plus a trace of cassiterite Tio 1.8 1.8 l:8 11s (SnO Heat treatments at 950C. or higher resulted in 3% i8 positive expansions. Neither glass could be crystallized Molar Ratio by heat treating at 850C. or lower temperatures for as -5 5.5 55 long as 16 hours. Attempts to obtain surface stress data mfg 2 31 04 078 L0 L2 for these glasses failed because the samples exhibited Copper oxide massed as cuov no compressive stress layer or they shattered during the heat treatment. Compositions l5 and 16 formed transparent glass- Vanadium pentoxide V 0 was also used as a nuceramics having a high quartz solid solution crystalline cleating agent since it is known that the vanadium ions phase wherein the coefficient of thermal expansion is exist in four different valence states; namely, 2, 3, 4,, substantially lower than that of the parent glass and a and 5. Heat treatments made on glasses 13 and 14 indicompressive stress layer was readily formed on each cated that the crystallization of the glasses can only be surface to a substantial depth. Compositions 17 and 18 initiated from the surface. The rate of crystallization is on heat treatment will not form transparent glassvery rapid since inch glass rod samples were fully 20 ceramics of the type discussed above, and compressive crystallized in less tharl hour Due to the absence of stress layers cannot be formed thereon.

Heat Treatment Conditions properties Heating Holding Comp. Rate Temp. Time AtmosaXlO Stress ep N0. (C./hr.) (C.) (hrs.) phere (0-300 C.) (p.s.i. X 10) (pm) v 15 320 850 4 Rd. 4.1 30.2c so 16 max. 825 l 99N2 -8.6 58.5C 137 bulk nucleation, samples heated in a hydrogen atmo- In the preferred embodiment of the invention, the sphere produced either a tension layer on the surface thermal in situ crystallization process is an isothermal :or shatteredjAlso, a very high degree of shrinkage ocheat treatment wherein the thermally crystallizable :curred during the heat treatment as a result of crystalliglass is heated at a predetermined rate to a holding zation. It is quite apparent, therefore, that vanadiumtemperature and maintained at such temperature for nucleated glasses are not suitable for the reducing the P ri of time necessary to have the desired comatmosphere-strengthening process of the present inv npressive stress layer formed on the surface of the resulttion I V n I V v D V ing transparent glass-ceramic to a depth of at least while applicant does no wish to be limited to any about 100 microns up to a depth of 400 or 500 microns particular explanation as to the mechanism involved in f more of course h coefhcleht thermal expah' forming compressive stress layers on glass-cera sion of the glass-ceramic should be within the range of dies by heat treating the thermally crystallizable glass h h +12 to l2 X 104 and Preferably containing a nucleating agent which can be reduced the range of from +6 to 6 X from a higher to a lower valence state and which is The usually most Preferreh are thosehavms a 0 i l X more effective at such lower valence state in a reducing 10a (On-300C) expahsloh cqefficlent shce these atmosphere, it is believed that the mechanism is one of hay? t best thermal i a edifferential crystallization. Thus, by selecting a ther- The thermally crystallizable glass can be subjected to mally crystallizable glass which can be thermally in situ a multistage heat treatment instead of the preferred iso crystallized to a glass-ceramic having a high quartz thermal heat treatment discussed above. However, it is solid solution crystalline phase and having a mu h critical, in order to develop the compressive stress layer lower thermal expansion than that of the parent glass, n the sur ace f the resulting glass-ceramic to an apa faster rate of nucleation can be induced in the surface P le dep h, hat the nucleating stage of the heat and just below the surface of such glass-ceramic, resulttreating pr s be conducted in a reducing atmoing in a greater degree of crystallization in that nucle- Where When u eation Occurs in an oxygen or air atd area as compared to h i i f h l mosphere no compressive stress layer is formed on the ceramic. Thus, a compressive stress layer is produced surface of the resulting glass-ceramic, even though the on the urfa e b the in d r t lli ti t i subsequent step of crystallization or crystal growth ocand just below the glass surface, which increased rate' Qhfflf] f? dueing Q P results higher degree of F h Y up to 3 times Table VlII gives the expansion and stress data for a or j the surface than the mtehor of the glass two-stage heat treatment and demonstrates that the nuhh hhha cleation phase of the process, which with these glasses To show the relationship of the Li O/Al O ratio in occurred at 750C, is significantly influenced by the the thermally crystallizable glass compositions suitable heat treatment in the reducing atmosphere. Three of for heat treating in a reducing atmosphere, the followthe first four glass samples in Table Vlll were nucleated ing glasses were prepared:

in a forming gas atmosphere at a holding temperature of 750C, while one was nucleated in air at 750C, for the times indicated in Table VI and subsequently crystallized at the indicated temperatures in air for the times indicated. A heat-up rate of 320C./hour was utilized to heat the glasses to the holding temperature.

TABLE Vlll (All Glasses-Composition Nucle- Crystallization Comp.

ution Heat Treatment 0-300C. Stress Depth Time Temp, Time (1X10 psi X pm hours C. hours I 37.8 25.0 35 l 825 l 3.7 3.1 200 l' 825 l 17.3 l 850 l 7.l 24.0 145 None 825 l 38.7 None 825 2 39.0 None 850 1 38.7 None 850 2 39.l

' Glass nucleated in air instead of forming gas at 750C. No compressive stress layer formed.

To show that the finishing heat treatments were not solely responsible for the crystallization, separate samples were heated isothermally at the finishing temperature and above of the previous heat reatments. These are the last four samples listed in Table Vlll. The expansion data obtained indicate that all such samples remained vitreous.

To further illustrate the effect of the reducing atmosphere during nucleation on compressive stress layer formation in the resulting product, a sample of Composition No. 5 glass was nucleated at 750 C. for 1 hour in air and finished at 825 C. for 1 hour, also in air. The expansion coefficient for this sample was 17.3 X l0 /C. (0 300C), and no compressive stress layer was formed. What occurs when all conditions remain the same except that a reducing atmosphere is used, is seen in Table Vlll, second glass-ceramic composition.

High-strength glass-ceramics of the present invention can be used in a variety of ways to make products wherein high mechanical strengths, good thermal shock resistance, and chemical durability are important, such as pipes for transporting chemicals and fluids, pumps and pump components, cookware, automobile and aircraft Windshields and windows, deep submergence vessels, and the like. Because of the high compressive stress layer which can be formed, products formed of the glass-ceramics of the invention are frangible and can be made to self-destruct into harmless particles upon strong impact instead of breaking into several large, jagged pieces which could cause severe damage immediately after impact. Airplane canopies are examples of such frangible glass-ceramics. Work done with these glass-ceramics shows that they have corrosion resistance and chemical durability properties substantially equivalent to those glass-ceramics commercially used today.

Having defined the invention, what is claimed is:

1. A transparent glass-ceramic body having a compressive stress layer on its surface up to a depth of about 500 microns which compressive stress is at least 20,000 psi, and a coefficient of thermal expansion of i 12 X l0 /C. (0-300C), said glass-ceramic body having a high quartz solid solution phase and formed by thermal in situ crystallization of a thermally crystallizable glass body having a coefficient of thermal expansion greater than that of said glass-ceramic, said glass body comprising at least 90 percent by weight of the following essential ingredients present in the indicated ranges:

Ingredient Weight Percent SiO, 54-76 A1 0 18-3] Li,0 241.4 Nucleating Agent 3-K CuO 0.5-6

wherein the nucleating agent is selected from the group consisting of TiO ZrO and mixtures thereof. and when said agent is TiO or ZrO alone it is present in an amount of from 3 to 6 weight percent, the molar ratio of SiO /Al O is from 3 to 6 and the molar ratio of Li O/Al O is from about 0.3 to about 0.9.

2. The transparent glass-ceramic body as defined in claim I wherein said CuO is present in an amount of from about I to about 3.5% by weight.

3. The glass-ceramic body as defined in claim 1 wherein the depth of said compressive stress layer is from about 100 to about 400 microns and the compressive stress is from about 20,000 to 80,000 psi.

4. The glass-ceramic body as defined in claim 3 wherein the difference in expansion coefficient between the glass and glass-ceramic bodies is at least 20 X l0 "/C. (0-300C).

5. A transparent glass-ceramic body having a compressive stress layer on its surface up to a depth of about 500 microns which compressive stress is at least 20,000 psi, and a coefficient of thermal expansion ofi 12 X 10"/C. (0-300C), said glass-ceramic body having a high quartz solid solution phase and formed by thermal in situ crystallization of a thermally crystallizable glass body having a coefficient of thermal expansion greater than that of said glass-ceramic, said glass body comprising at least percent by weight of the following essential ingredients present in the indicated ranges:

Ingredient Weight Percent SiO, 57-69 M 0, 20-31 Li o 3-6 Nucleating Agent 3-l0 CuO l5 wherein the nucleating agent is selected from the group consisting of TiO ZrO and mixtures thereof, the SiO /Al O molar ratio is from 3.2 to 5.5 and the Li O/AI O molar ratio is from 0.4 to about 0.8.

6. The glass-ceramic body as defined in claim 5 wherein the depth of said compressive stress layer is from about to about 400 microns and the compressive stress is from about 20,000 to 80,000 psi.

7. A transparent glass-ceramic body having a compressive stress layer on its surface and having a coefficient of thermal expansion of: 12 X l0"/C (0-300C), said glass ceramic body having a high quartz solid solution phase and formed by thermal in situ crystallization of a thermally crystallizable glass body having a coefficient of thermal expansion greater than that of said glass-ceramic, said glass body comprising at least 90 percent by weight of the following essential ingredients present in the indicated ranges:

Ingredients Weight Percent SiO, 54-76 Al O Iii-33 Li,O 26.4 Nucleating Agent 3-H Metal Oxide 0.5-6

wherein said metal oxide is selected from the group consisting of copper oxide expressed as CuO and iron V V 14V and the molar ratio of Li O/Al O is from about 0.3 to about 0.9.

8. A transparent glass-ceramic body of claim 7 wherein said metal oxide is iron oxide.

UNITED STATES PATENTAND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT N0. 3,779,856

DATED December 19, 1973 INVENTOMS) I Perry F. Pirooz it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: O

Column 11, line 61 and 62 12" should be +12 to -l2.

Column 12, lines 28 and 29 12" should be +12 to -l2. Q r Column 12, line 52 "12" should be +12 to -12.

Signed and Scaled this Fifteenth D y f February 1977 [SEAL] Arrest:

p-"6 c. MARSHALL DANN Office Commissioner ofParems and Trademarks UNITED STATES PATENT ()FFICE CERTIFICATE OF CORRECTION Patent No. 3 779 ,856 Dated December 18 1973 Inventor(s) Perry P. Pirooz It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column line 38, "treated" should be ---heated---. Column 5, line 61, "he" should be ---the---. Column 11, line 2 "reatments" should be ---treatments---.

Signed and Scaled this twenty-third Of March 1976 [SEAL] A ttest:

RUTH C. MA SON C. MARSHALL DANN Arresting Officer (ommisximzer oj'ParenIs and Trademarks 

2. The transparent glass-ceramic body as defined in claim 1 wherein said CuO is present in an amount of from about 1 to about 3.5% by weight.
 3. The glass-ceramic body as defined in claim 1 wherein the depth of said compressive stress layer is from about 100 to about 400 microns and the compressive stress is from about 20,000 to 80,000 psi.
 4. The glass-ceramic body as defined in claim 3 wherein the difference in expansion coefficient between the glass and glass-ceramic bodies is at least 20 X 10 7/*C. (0*-300*C.).
 5. A transparent glass-ceramic body having a compressive stress layer on its surface up to a depth of about 500 microns which compressive stress is at least 20,000 psi, and a coefficient of thermal expansion of + or - 12 X 10 7/*C. (0*-300*C.), said glass-ceramic body having a high quartz solid solution phase and formed by thermal in situ crystallization of a thermally crystallizable glass body having a coefficient of thermal expansion greater than that of said glass-ceramic, said glass body comprising at least 90 percent by weight of the following essential ingredients present in the indicated ranges: IngredientWeight Percent SiO257-69 Al2O320-31 Li2O3-6 Nucleating Agent3-10 CuO1-5 wherein the nucleating agent is selected from the group consisting of TiO2, ZrO2 and mixtures thereof, the SiO2/Al2O3 molar ratio is from 3.2 to 5.5 and the Li2O/Al2O3 molar ratio is from 0.4 to about 0.8.
 6. The glass-ceramic body as defined in claim 5 wherein the depth of said compressive stress layer is from about 100 to about 400 microns and the compressive stress is from about 20,000 to 80,000 psi.
 7. A transparent glass-ceramic body having a compressive stress layer on its surface and having a coefficient of thermal expansion of + or - 12 X 10 7/*C (0*-300*C), said glass ceramic body having a high quartz solid solution phase and formed by thermal in situ crystallization of a thermally crystallizable glass body having a coefficient of thermal expansion greater than that of said glass-ceramic, said glass body comprising at least 90 percent by weight of the following essential ingredients present in the indicated ranges: Ingredients Weight Percent SiO254-76 Al2O318-33 Li2O2-6.4 Nucleating Agent 3-8 Metal Oxide0.5-6 wherein said metal oxide is selected from the group consisting of copper oxide expressed as CuO and iron oxide expressed as Fe2O3 and the nucleating agent is selected from the group consisting of TiO2, ZrO2 and mixtures thereof, and when said agent is TiO2 or ZrO2 alone it is present in an amount of from 3 to 6 weight percent, the molar ratio of SiO2/Al2O3 is from 3 to 6 and the molar ratio of Li2O/Al2O3 is from about 0.3 to about 0.9.
 8. A transparent glass-ceramic body of claim 7 wherein said metal oxide is iron oxide. 